What is an isomer?

What is an isomer?

• A. Same molecular formula but different structure
• B. Different molecular formulas with same mass
• C. Two molecules that react to form water
• D. A type of carbohydrate

Answer: (A)

Isomers are molecules that share the same molecular formula but differ in how the atoms are arranged, either in how they are connected or in their three-dimensional orientation. This difference in structure leads to distinct properties even though the overall counts of carbon, hydrogen, and oxygen (and other elements) are the same. The statement that describes this idea—having the same molecular formula but a different arrangement of atoms—is exactly what is meant by isomers, so it’s the best choice. Two helpful examples: glucose and fructose both have the formula C6H12O6, but their atoms are arranged differently, giving them different structures and properties. The other statements don’t fit the concept: having different formulas with the same mass isn’t isomerism, a reaction that forms water describes a chemical reaction rather than a structural relationship, and an isomer is not a type of carbohydrate.

Isomers are molecules that share the same molecular formula but differ in how the atoms are arranged, either in how they are connected or in their three-dimensional orientation. This difference in structure leads to distinct properties even though the overall counts of carbon, hydrogen, and oxygen (and other elements) are the same.

The statement that describes this idea—having the same molecular formula but a different arrangement of atoms—is exactly what is meant by isomers, so it’s the best choice.

Two helpful examples: glucose and fructose both have the formula C6H12O6, but their atoms are arranged differently, giving them different structures and properties.

The other statements don’t fit the concept: having different formulas with the same mass isn’t isomerism, a reaction that forms water describes a chemical reaction rather than a structural relationship, and an isomer is not a type of carbohydrate.